1. Field of the Invention
The present invention relates in general to a method of supplying a suction nozzle with electric components (including electronic components), and an electric-component mounting system arranged to mount the electric components on a circuit substrate such as a printed-wiring board, and more particularly to techniques for reducing a failure of the suction nozzle to hold the electric components by suction.
2. Discussion of Related Art
A suction nozzle is arranged to hold an electric component by suction under a reduced or negative pressure, and is used in an electric-component mounting system, for example. In the electric-component mounting system, the electric component is supplied from a component supply device, and is held by the suction nozzle, so that the electric component is mounted on a circuit substrate. The suction nozzle is arranged to receive the electric components from the component supply device, at a predetermined component receiving position, but may suffer from a sucking failure, that is, a failure to correctly hold the electric component by suction, such as a failure to receive the electric component.
The sucking failure takes place due to inadequate positioning of the electric component with respect to the suction nozzle upon sucking of the electric component by the suction nozzle, a positioning error of the component supply device and a positioning error of a component-holding head which holds the suction nozzle. An adequate sucking position of the electric component at which the electric component can be sucked by the suction nozzle with high stability changes with the specific shape and size of the electric component, and may deviate from the center position of the electric component. The inadequate positioning error of the electric component with respect to the suction nozzle may be caused when the component supply device and the suction nozzle are positioned relative to each other such that the electric component is always sucked at its central portion by the suction nozzle. The positioning errors of the component supply device and the component-holding head may be caused by manufacturing and assembling errors and local thermal expansion of the component supply device, the component-holding head and the related devices. In view of the above, it has been a conventional practice to determine the sucking position of the electric component depending upon the specific kind of the electric component, obtain the positioning errors of the component supply device and the component-holding head, and position the sucking surface of the suction nozzle and the component supply device relative to each other, on the basis of the determined sucking position and the obtained positioning errors, for thereby reducing the inadequate positioning of the electric component with respect to the suction nozzle.
However, the conventional practice still suffers from the sucking failure due to inadequate positioning of the electric component with respect to the sucking surface of the suction nozzle. Where the suction nozzle includes a suction pipe whose end face functions as the sucking surface, for example, a bending of the suction pipe causes a positional deviation of the sucking surface with respect to the electric component, resulting in the sucking failure, such as a failure to receive the electric component or inadequate holding of the electric component that cannot be corrected. Conventionally, bending of the suction pipe is detected to check whether the suction pipe if bent can be used for mounting the electric component, or whether the bent suction pipe should be replaced with a new one. This detection of the bending of the suction pipe is affected for the purpose of avoiding the use of the defective suction nozzle for mounting the electric component. However, the bending of the suction pipe is not conventionally taken into account when the electric component is sucked by the suction nozzle. This is one of the reasons for the sucking failure in the prior art.
The present invention was made in view of the problems encountered in the prior art described above. It is therefore an object of the present invention to reduce a failure of the suction nozzle to correctly hold the electric component by suction, in a method of transferring the electric component from the component supply device to the suction nozzle, and an electric-component mounting system arranged to mount the electric component on a substrate.
The above object may be achieved according to any one of the following modes of the present invention in the form of a method of supplying a suction nozzle with an electric component and an electric-component mounting system. Each of the following modes of the invention is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A method of controlling an operation in which electric components are transferred one after another from a component supply device to a suction nozzle which is held by a component-holding head rotatable about an axis of rotation thereof, such that the suction nozzle extends in an axial direction of the component-holding head, each of the electric components being held by the suction nozzle by suction on a sucking surface provided at a free end of the suction nozzle, the method comprising:
a relative-position obtaining step of obtaining a relative position between the sucking surface and the axis of rotation of the component-holding head;
a relative-movement step of effecting a relative movement between the component-holding head and the component supply device on the basis of the relative position obtained in the relative-position obtaining step, so as to minimize an error of relative positioning between the sucking surface and a predetermined sucking position of the electric component positioned at the component-supply portion; and
a component supply step of moving, after the relative movement between the component-holding head and the component supply device in the relative-movement step, the component-holding head and the component supply device toward each other, for transferring one of the electronic components from the component supply device to said suction nozzle.
In the absence of a positioning error of the sucking surface with respect to the axis of the component-holding head (hereinafter referred to simply as xe2x80x9chead axisxe2x80x9d), there is established a predetermined relative position between the predetermined sucking position of the electric component and the head axis, so that there is established a predetermined relative position between the sucking surface and the predetermined sucking position, when the electric component (typically, an electronic component) is transferred from the component-supply portion to the suction nozzle. In the presence of a positioning error of the sucking surface with respect to the head axis, on the other hand, there exists a positioning error between the sucking surface and the predetermined sucking position of the electric component positioned at the component-supply portion. This positioning error between the sucking surface and the predetermined sucking position corresponds to the positioning error between the sucking surface and the head axis. Where the angular position of the component-holding head in which the relative position between the sucking surface and the head axis is obtained is the same as the angular position in which the electric component is transferred from the component-supply portion to the suction nozzle, the relative positioning error between the sucking surface and the predetermined sucking position of the electric component when the electric component is transferred from the component-supply portion to the sucking surface can be obtained on the basis of the obtained relative position between the sucking surface and the head axis. Accordingly, the sucking failure of the suction nozzle can be reduced, by moving the component-holding head and the component-holding device relative to each other so as to minimize the relative positioning error between the sucking surface and the predetermined sucking position.
The method according to the above mode (1) of this invention is effective particularly where the suction nozzle includes a suction pipe which has the sucking surface at its free end and which may have some degree of bending. According to the present method, the component-holding head and the component supply device are positioned relative to each other so as to minimize the error of relative positioning between the sucking surface and the component-supply portion, even in the presence of a relative positioning error between the sucking surface and the head axis, which is caused by bending of the suction pipe. When the electric component is transferred from the component-supply portion to the suction nozzle, the amount and direction of the relative positioning error which may be caused by the bending of the suction pipe are obtained, and the component-holding head and the component supply device are positioned relative to each other on the basis of the obtained relative positioning error, so as to minimize this error. The present method is effective to prevent a sucking failure of the suction nozzle even where the electric component is relatively small and the suction pipe has some degree of bending and/or positioning error.
(2) A method according to the above mode (1), wherein the relative-position obtaining step, the relative-movement step and the component supply step are affected when the component-holding head is placed in a same angular position thereof.
(3) A method according to the above mode (1), wherein the relative-position obtaining step, the relative-movement step and the component supply step are affected when said component-holding head is placed in a predetermined angular position thereof.
(4) A method according to any one of the above modes (1)-(3), wherein the relative-position obtaining step comprises:
a first image-taking step of operating an image-taking device to take a first image of the sucking surface in an axial direction of the component-holding head toward the sucking surface;
a rotating step of rotating the component-holding head about the axis of rotation by a predetermined angle;
a second image-taking step of operating the image-taking device to take a second image of the sucking surface; and
an obtaining step of obtaining a position of the axis of rotation of the component-holding head on the basis of at least the first and second images of the sucking surface taken in the first and second image-taking steps, and obtaining the relative position between the sucking surface and the axis of rotation.
The first imaging angular position in which the first image of the sucking surface is taken in the first image-taking step and the second imaging angular position in which the second image of the sucking surface is taken in the second image-taking step may both be different from the predetermined angular position in which the electric component is transferred from the component-supply portion to the suction nozzle, or one of the first and second imaging angular positions may be the same as the predetermined angular position, as in a method according to the following mode (5). The position of the axis of rotation of the component-holding head may be obtained on the basis of at least one additional image of the sucking surface as well as the first and second images taken in the first and second image-taking steps.
The center points of the first and second images of the sucking surface taken at the first and second angular positions of the component-holding head lie on a circle having its center on the axis of rotation of the component-holding head. The position of the axis of rotation of the component-holding head is obtained by calculation on the basis of the center points of the first and second images of the sucking surface and the first and second imaging angular positions with respect to a predetermined angular zero position of the head, namely, angular differences of the first and second imaging angular positions with respect to the angular zero position.
Where one of the first and second imaging angular positions is the same as the predetermined angular position, the first or second image of the sucking surface is taken in the angular position of the component-holding head in which the electric component is transferred from the component-supply portion to the suction nozzle. In this case, the positioning error between the center point of the image of the sucking surface taken in the predetermined angular position of the head and the obtained position of the axis of rotation of the head does represent the positioning error between the center point of the sucking surface and the axis of rotation of the head placed in the predetermined angular position. Accordingly, the calculation to obtain the position of the axis of rotation of the head is simplified. Where the first and second imaging angular positions are both different from the predetermined angular position, the center point of the sucking surface when the component-holding head is placed in its predetermined angular position lies on the circle on which the center points of the first and second images of the sucking surface lie. Therefore, the center point of the sucking surface when the head is placed in the predetermined angular position can be calculated on the basis of the known first and second imaging angular positions and the predetermined angular position with respect to the angular zero position of the head, and the center points of the first and second images of the sucking surface. Thus, the relative position between the center point of the sucking surface in the predetermined angular position of the head and the axis of rotation of the head can be obtained. In this case, however, the required calculation is relatively complicated and time-consuming.
(5) A method according to the above mode (4), wherein one of the first and second images of the sucking surface is taken when the component-holding head is placed in a predetermined angular position thereof.
(6) A method according to any one of the above modes (1)-(5), wherein the relative-movement step comprises moving the component-holding head to a predetermined position along a circular arc, and moving the component-supply portion of the component supply device in a direction of tangency to the circular arc.
According to the above mode (6) of this invention, the positioning error between the sucking surface and the predetermined sucking position of the electric component positioned at the component-supply portion is substantially zeroed in the direction of movement of the component-supply portion, by moving the component-supply portion.
(7) A method according to any one of the above modes (1)-(6), wherein the electric component is transferred from the component-supply portion of the component supply device to the suction nozzle held by a selected one of a plurality of component-holding heads, and a relative movement between the selected component-holding head and the component supply device is affected in the relative-movement step, on the basis of a relative positioning error of the axes of rotation of the plurality of component-holding heads, as well as the relative position obtained in the relative-position obtaining step. For instance, the relative movement between the selected component-holding head and the component supply device is affected on the basis of a positioning error of the axis of rotation of the selected component-holding head with respect to the axis of ration of a reference component-holding head which is selected from the plurality of heads.
(8) A method according to any one of the above modes (1)-(7), wherein the relative movement between the component-holding head and the component supply device is affected in the relative-movement step, on the basis of a positional difference between the predetermined sucking position of the electric component and a center of the component-supply portion when the electric component is ready to be transferred from the component-supply portion to the suction nozzle, as well as the relative position obtained in the relative-position obtaining step.
(9) An electric-component mounting system for mounting electric components on a circuit substrate, comprising:
a component supply device having a component-supply portion from which the electronic components are supplied one after another;
a circuit-substrate support device for supporting the circuit substrate;
a component-holding head rotatable about an axis of rotation thereof and arranged to removably hold a suction nozzle having a sucking surface such that the suction nozzle extends in an axial direction of the component-holding head;
a head rotating device operable to rotate the component-holding head;
a relative-movement device operable to move the component-holding head, the component supply device and the circuit-substrate support device relative to each other, in a direction intersecting the axis of rotation of the component-holding head;
an axial-movement device operable to move the component-holding head and the component supply device in the axial direction toward and away from each other;
an image-taking device operable to take an image of the sucking surface in the axial direction toward the sucking surface; and
a control device operable to control the head rotating device, the relative-movement device, the axial-movement device and the image-taking device,
and wherein the control device includes
a relative-position obtaining portion operable to obtain a relative position between the sucking surface and the axis of rotation of the component-holding head;
a relative-movement control portion operable to control the relative-movement device, for effecting a relative movement between the component-holding head and the component supply device on the basis of the relative position obtained by the relative-position obtaining portion, so as to minimize an error of relative positioning between the sucking surface and a predetermined sucking position of the electric component positioned at the component-supply portion; and
a component-transfer control portion operable after the relative movement between the component-holding head and the component supply device by the relative-movement device, to control the axial-movement device to move the component-holding head and the component supply device toward each other, for transferring one of the electric components from the component-supply portion of the component supply device to the suction nozzle.
An electric-component mounting system may use a plurality of component-holding heads which, for example, are mounted on a rotating body rotatable about its axis, such that the component-holding heads are equiangularly spaced from each other along a circle having its center on the axis of rotation of the rotating body. The rotating body may be an indexing disk which is intermittently rotatable about its axis, or a rotary body which is rotatable in opposite directions by predetermined angles. The intermittently rotatable indexing disk is intermittently rotated by a suitable rotary drive device so that the component-holding heads are turned about the axis of rotation of the indexing disk, and are sequentially stopped at a plurality of working positions arranged along a circular path of turning movement. The component supply device is located at one of the working positions, while the circuit-substrate support device is located at another working position. The rotary body which is rotatable in the opposite directions by the predetermined angles is also rotated by a suitable rotary drive device so that the component-holding heads are turned about the axis of rotation of the rotary body, and are stopped at predetermined working positions. In either of these cases, the rotating body and the rotary drive device constitute the head rotating device indicated above.
The component-holding heads may be supported by respective support members which are arranged about a common axis of turning such that the support members can be turned about the common axis of turning, independently of each other. When the support members are turned about the common axis by a suitable turning device, the support members are sequentially stopped at one or more working positions, at a predetermined time interval. The component-holding heads are supported by the respective rotatable members such that the heads are spaced by the same distance from the common axis of turning. In this case, the support members and the turning device constitute a head moving device in the form of a head turning device operable to turn each component-holding head along a circular path.
The electronic-component mounting system may use at least one component-holding head mounted on a movable member which is linearly movable in a plane, in at least one of two mutually perpendicular directions. Where the movable member is movable by a positioning device in the two mutually perpendicular directions, each component-holding head can be moved to a desired position in the above-indicated plane. In this case, the movable member and the positioning device constitute a head moving device operable to move each component-holding head. The relative-movement device indicated above includes this head moving device.
The above-indicated rotating body and rotary drive device or the above-indicated plurality of support members and turning device may be mounted on a movable member which is movable in a plane in two mutually perpendicular directions. The axis of rotation of the rotating body or the common axis of turning of the support members may be perpendicular to the surface of the circuit substrate supported by the circuit-substrate support device, for instance, parallel to the vertical direction, or may be inclined with respect to the vertical direction. In this case, the relative-movement device indicated above includes the rotating body, the rotary drive device, the movable member and a positioning device for moving the movable member, or the support members, the turning device, the movable member and the positioning device.
The circuit-substrate support device may be stationary, or movable by a suitable positioning device to move and position the circuit substrate. In the latter case, the relative-movement device indicated above includes the positioning device to move the circuit substrate together with the circuit-substrate support device.
The component supply device may be stationary, or movable by a suitable positioning device to move the component supply device. In the latter case, the relative-movement device indicated above includes the positioning device to move the component supply device.
The component supply device, which is stationary or movable, includes a plurality of feeders, and a support block or table on which the feeders are mounted such that the component-supply portions of the feeders are arranged in s straight low. Each feeder accommodates a plurality of electric components of the same kind. Each feeder may be a tape feeder having a tape cartridge arranged to feed a carrier tape accommodating electric components, such that the electric components are fed one after another to the component-supply portion of the feeder. Alternatively, the feeder is arranged to feed a succession of electric components by means of a vibrator, a slideway, an air stream or a conveyor belt, or a combination thereof, such that the electric components are fed one after another to the component-supply portion. In either of these cases, the feeder includes a storage device accommodating the electric components, and a feeding device for feeding the electric components from the storage device to the component-supply portion.
Where the component supply device is movable, the support block or table supporting the feeders is moved by a table positioning device in a direction parallel to the direction of arrangement of the component-supply portions, so that the component-supply portion of a selected one of the feeders is located at a predetermined component supply position. The component-supply portions of the feeders may be arranged along a straight line, or any other lines such as a circle, a circular arc or a curve (other than the circular arc), or a combination thereof. The feeding device and the storage device of the movable component supply device may be mounted on a common support block or table, so that the feeding deice and the storage device are moved together when the common support block is moved. Alternatively, the feeding device and the storage device may be mounted on separate support blocks, respectively. In this case, the feeding device and the storage device may be mounted on respective movable support blocks so that the feeding device and the storage device are movable independently of each other. Alternatively, the storage device may be stationary.
The component supply device may be of tray type having a plurality of trays each having a multiplicity of component-accommodating recesses accommodating the respective electric components.
The image-taking device is arranged to take the image of the sucking surface of the suction nozzle in the axial direction of the component-holding head toward the sucking surface. The image-taking device may be a CCD camera, which may be disposed concentrically with the component-holding head such that the CCD camera is opposed to the sucking surface of the suction nozzle. Alternatively, the CCD camera and the component-holding head may be juxtaposed in parallel relationship with each other such that the CCD camera faces downwards. Where the CCD camera is not opposed to the sucking surface, as in the latter case, a waveguide device is provided to guide a light indicative of the image of the object (sucking surface) so as to be incident upon the CCD camera. In this case, the waveguide and the CCD camera constitute the image-taking device.
The image-taking device may be a surface-imaging device arranged to take a two-dimensional image of the object at one time, or a line sensor which includes a multiplicity of image-taking elements arranged in a straight line. In the line sensor, a two-dimensional image is formed by multiple lines of image which are taken successively while the line of the image-taking elements is moved relative to the object.
The electric-component mounting system constructed according to the above mode (9) of this invention provides substantially the same effects and advantages as described above with respect to the method according to the above mode (1). The feature according to the above mode (4) or (5) is applicable to the electric-component mounting system according to the above mode (9).
(10) An electric-component mounting system according to the above mode (9), wherein the relative-position obtaining portion, the relative-movement control portion and the component-transfer control portions are all operable when said component-holding head is placed in a predetermined angular position.
(11) An electric-component mounting system according to the above mode (9) or (10), wherein the relative-movement device comprises:
a head turning device operable to turn the component-holding head about a turning axis, such that the component-holding head can be sequentially stopped at a plurality of working positions which are arranged along a circular path of turning of the component-holding head; and
a component-supply-device positioning device operable to move the component supply device in a direction of tangency to the circular path of turning, to bring the component-supply portion into alignment with one of the working positions.
(12) An electronic-component mounting system according to any one of the above modes (9)-(11), wherein the relative-movement control portion is operable to control the component-supply-device positioning moving device for positioning the component supply device such that the error of relative positioning between the sucking surface and the predetermined sucking position of the electric component in the above-indicated direction of tangency is substantially zeroed.